Thanks for the reply. It seems to be an endian issue such that I can't simply shift bits but must use a proper framer.
I have modified an existing AX.25 block such that I can now see my frames over the air using debug prints but I am having difficulty getting my data out from gnuradio. The AX.25 block, from gr-ec, creates frames through several iterations of the work() fn using a state machine and also has a message queue output (but hasn't actually implemented the message passing). Once I have a verified frame, what is the best way to get the data out? I have tried this technique: d_good_byte_cnt += frame_size-2; // don't count CRC gr_message_sptr msg = gr_make_message(0, 0, 0, d_good_byte_cnt); memcpy(msg->msg(), frame_buf, d_good_byte_cnt); d_target_queue->insert_tail(msg); msg.reset(); and then connect to a message source, and then a file sink. However, the memcpy seems to cause my flowgraph to crash. Any tips? On Wed, Nov 6, 2013 at 1:42 AM, Tom Rondeau <[email protected]> wrote: > On Mon, Nov 4, 2013 at 10:25 AM, Vanush Vaswani <[email protected]> wrote: >> Hi all, >> >> I am using GR 3.6.5.1 to receive BPSK modulated data from a third >> party RF chip / microcontroller combination and am having a strange >> experience. I am implementing a very simple protocol by constantly >> transmitting 0x7E constantly and then ASCII data triggered by a serial >> connection to the microcontroller, all at 9.6kbps >> >> With the following configuration >> FCDPP source sampling at 192KHz. >> -> AGC >> -> Freq Xlate (bring near baseband) >> -> Costas loop (remove carrier) >> -> RRC (48 taps, symbol rate = 9600) >> -> PSK Demod (sps = 20 as 192/20 = 9.6kbps, everything else default) >> >> I can see my 0x7E bitstream "square wave" in a scope sink. >> When I pack the bits and send it to a file sink, I can see my 0x7E's >> and also ascii data that I've typed in to the microcontroller serial >> port. However - this is rare. Most of the time, I see the bytes of >> rotated flag - 0x3F, 0xFC, 0x3F etc. I thought this was ok, I can >> simply rotate the whole file by x bits to remake all the flags as >> 0x7E. But when I do this, my ascii text input is completely garbled, >> with only a few letters showing up. >> >> Can anyone give me a hint as to what is going on? I don't think my >> transmitter is the issue, as when I get my flag bytes in the output >> file, I can see my data. >> >> vanush > > The PSK demod has the FLL, Costas loop, and RRC filter in it. That's > what each of those bandwidth settings are for (frequency, phase, and > timing). But also, going in at 20 sps is really high. You should put a > channel filter in front that both removes any extra noise and > downsamples (by a factor of 5 or 10 to get to 4 or 2 sps). > > Tom _______________________________________________ Discuss-gnuradio mailing list [email protected] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
